fix(webdav): reject PROPPATCH on protected DAV:/oc:/nc:/ocs: props

DeadPropertyStore let PROPPATCH set any namespace/name verbatim,
incl. names the server itself emits as live state (DAV: entirely,
plus oc:/nc:/ocs: names used by write_file_response /
write_folder_response). That either forges a live prop or stores
dead rows nothing ever reads. is_protected_property() denylists
them; both PROPPATCH handlers (native + NC) now return per-property
403 instead of storing. oc:favorite stays writable via its existing
special-case, which runs before the protection check.

src/application/adapters/webdav_adapter.rs

@@ -72,6 +72,46 @@ impl std::fmt::Display for QualifiedName {
     }
 }
 
+/// Whether PROPPATCH must refuse to set/remove this property as a dead
+/// property (RFC 4918 §9.2 — server MAY reject a PROPPATCH attempt on a
+/// live property; DeadPropertyStore has no business holding a value that
+/// PROPFIND / REPORT already emit from live server state).
+pub fn is_protected_property(qn: &QualifiedName) -> bool {
+    match qn.namespace.as_str() {
+        // RFC 4918 §15 — the DAV: namespace is server-owned in its
+        // entirety. Any PROPPATCH into it either forges a live
+        // property (dual-emission) or accumulates unread garbage
+        // (silent litter).
+        "DAV:" => true,
+
+        // Every name below appears verbatim in write_folder_response
+        // / write_file_response in the NC handler. Adding a new
+        // live emitter → add its name here.
+        "http://owncloud.org/ns" => matches!(
+            qn.name.as_str(),
+            "favorite"
+                | "fileid"
+                | "id"
+                | "owner-id"
+                | "owner-display-name"
+                | "permissions"
+                | "share-types"
+                | "size"
+        ),
+
+        "http://nextcloud.org/ns" => matches!(
+            qn.name.as_str(),
+            "has-preview" | "is-encrypted" | "mount-type" | "creation_time" | "upload_time"
+        ),
+
+        "http://open-collaboration-services.org/ns" => {
+            matches!(qn.name.as_str(), "share-permissions")
+        }
+
+        _ => false,
+    }
+}
+
 /// PROPFIND request type
 #[derive(Debug, PartialEq)]
 pub enum PropFindType {